1. Field of the Invention
The present invention relates to an apparatus and method for preventing noise, and more particularly, to an apparatus and method for preventing noise in a touch screen.
This application claims foreign priority to, and is based on, Korean Patent Application No. 2002-72694, the contents of which is incorporated herein by reference.
2. Description of the Related Art
FIG. 1 is a diagram of the structure of a related art apparatus for preventing noise in a touch screen, including a touch screen panel 11, a touch screen control unit 12, a central control unit 13, a liquid crystal display (LCD) control unit 14, and an LCD panel 15.
The touch screen panel 11 is an input device. The touch screen control unit 12 reads x and y coordinates of the touch screen. The central control unit 13 controls the entire related art system. The LCD control unit 14 controls the LCD panel. The LCD panel 15 is a video output device. In general, the touch screen control unit 12 and the LCD control unit 14 are controlled separately by the central control unit 13, and in some systems a liquid crystal driving signal is used.
The touch screen control unit 12 converts analog-type x and y voltage values of the touch screen by an external input into digital values and sends the digital values to the system CPU. At this time, the x and y voltage values are analog values that are very sensitive to external noise. The biggest influence on the analog values is signals generated by a most closely located LCD.
However, the related art has various problems and disadvantages. For example, but not by way of limitation, when a video is displayed in an LCD display panel, gates in the panel are turned on, a liquid crystal driving signal is output, and the LCD panel displays a video. At this time, a large voltage is provided momentarily, and glitch noise is generated.
Since the aforementioned glitch noise affects the touch screen panel voltage, an accurate voltage value cannot be obtained. To reduce glitch noise, the touch screen control unit 12 monitors the liquid crystal driving signal and operates the touch screen panel only when the liquid crystal driving signal does not operate. By doing so, the noise generated by the LCD is eliminated. However, as the LCD panel has evolved to a high resolution color LCD, the speed of the liquid crystal driving signal has increased greatly, and it has become impossible to monitor the liquid crystal driving signal and operate the touch screen with the related art high resolution color LCD.
As another method to prevent noise, the LCD panel itself is grounded so that excitation of LCD noise to the outside is prevented. However, this method cannot prevent noise completely because of different noise characteristics and operation voltages.
In addition, since the above related art methods need addition of a noise elimination circuit to the LCD panel itself or mechanical shielding, substantial cost accrues. Further, due to irregular results, a huge amount of development time is required.